WO2025115510A1 - Dental-use curable composition, inorganic powder granular body, and method for producing same - Google Patents

Abstract

This dental-use curable composition contains: a polymerizable monomer (M); and a specific inorganic powder granular body (C) constituted from aggregated particles (c) composed of: inorganic particles (a) that constitutes an inorganic powder/granular body (A) having a specific average particle diameter and zeta potential; and inorganic particles (b) that constitutes an inorganic powder/granular body (B) having a specific average particle diameter and zeta potential. The dental-use curable composition further contains at least one selected from the inorganic powder/granular body (A) and a specific organic/inorganic composite powder/granular body (D), and the content of each of the powder/granular bodies is in a specific range.　The present invention successfully provides a dental-use curable composition that demonstrates high dispersibility of an inorganic powder granular body in the composition and good discharge properties from a syringe, that has adequate fluidity, that exhibits little change in fluidity over time and that has high mechanical strength after curing.

Description

Dental hardenable composition, inorganic powder and its method of manufacture

The present invention relates to a dental hardenable composition, an inorganic powder and a method for producing the same.

Dental hardenable compositions contain as their main components a polymerizable monomer, an inorganic filler consisting of an aggregate of inorganic particles (inorganic powder), and a polymerization initiator. Among these, composite resins are one of the most widely used materials in dental treatment as a material for repairing cavities after removing tooth defects or caries.

Composite resins are required to have excellent workability in a paste state before polymerization and hardening, and excellent aesthetics and physical properties such as mechanical strength of the hardened product obtained after polymerization and hardening.
In recent years, a flowable composite resin has been developed in which a needle with a small hole, called a needle tip, is attached to a syringe containing composite resin paste, allowing the paste to be filled directly into the cavity from the tip of the needle.This type of flowable composite resin is now being used more widely in clinical settings because it makes tooth repair easier.

The above flowable composite resin is required to have good operability when filling cavities etc., specifically, good ejection properties when ejected from a syringe equipped with a needle tip, and to have appropriate fluidity in a paste state according to the case. For example, if the fluidity is too high in the paste state, the paste will tend to drip and its formability (the ability to maintain its shape and not easily deform due to natural flow when left to stand) will be poor, so it is necessary for it to have appropriate fluidity.

Fullable composite resin has a relatively low inorganic powder content, which increases its fluidity and improves ejection from a syringe, but the high fluidity can make it difficult to obtain moldability.

In response to such problems, Patent Document 1 discloses a technique for improving various physical properties of a composite resin by using two types of inorganic powders in a specific ratio, each of which exhibits a zeta potential (in water) of opposite polarity and has a specific average particle size and specific surface area. In the examples, it is described that a dental curable composition containing a polymerizable monomer, a silica-based composite oxide having an average particle size of 50 nm to 1 μm, and a crystalline rare earth metal fluoride having a specific surface area of 25 to 100 m ² /g has good ejectability (has a consistency suitable for ejection from a syringe) and exhibits appropriate fluidity that suppresses dripping of the paste.

International Publication No. 2023/085201

As described above, Patent Document 1 discloses that a dental hardenable composition (paste-like) having appropriate fluidity can be obtained by using in combination a silica-based composite oxide and a crystalline rare earth metal fluoride, which have different zeta potential polarities.
However, Patent Document 1 does not consider changes in fluidity of the dental hardenable composition over time. According to the study by the present inventors, it was found that the dental hardenable composition described in Patent Document 1 may become highly fluid and may no longer exhibit appropriate fluidity when stored for a long period of time (for example, about one week at 50° C.).

Therefore, an object of the present invention is to provide a dental hardenable composition which has high dispersibility of inorganic powder particles in the composition, good dischargeability from a syringe, appropriate fluidity, and which exhibits little change in fluidity over time, and has high mechanical strength after hardening.
Another object of the present invention is to provide an inorganic powder or granule which has good dispersibility when blended in a dental hardenable composition, and a method for producing the same.

The present inventors have conducted extensive research to achieve the above object. As a result, they have found that the above problem can be solved by a dental curable composition that contains a polymerizable monomer (M) and a specific inorganic powder (C) composed of inorganic particles (a) constituting an inorganic powder (A) having a specific average particle size and zeta potential, and agglomerated particles (c) composed of inorganic particles (b) constituting an inorganic powder (B) having a specific average particle size and zeta potential, and further contains at least one type selected from the inorganic powder (A) and a specific organic-inorganic composite powder (D), and the content of each powder falls within a specific range, and thus the present invention has been completed.

The gist of the present invention is the following [1] to [12].
[1] 100 parts by mass of a polymerizable monomer (M), and an inorganic powder (C) comprising agglomerated particles (c) including a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential when measured in water, and an average primary particle diameter measured by an electron microscope of 50 nm to 1 μm, and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, and an inorganic powder (B) comprising an aggregate particle (c) including the inorganic particles (b),
the average value of the total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) contained in each of the aggregate particles (c) constituting the inorganic powder or granule (C) is within a range of 20 to 300 parts by mass;
Inorganic powder or grain (C): 10 to 100 parts by mass, having an average agglomerated particle size of 1 to 50 μm, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method;
A composition comprising:
The composition further comprises at least one of the inorganic powder (A) and the organic-inorganic composite powder (D),
the organic-inorganic composite powder (D) is constituted by organic-inorganic composite particles (d) made of a composite material of the inorganic powder (A) and a resin, the content of the inorganic powder (A) in the composite material being 60 to 90 mass %, and the organic-inorganic composite powder (D) has an average particle size of 1 to 100 μm, which is defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method;
A dental curable composition, characterized in that a total content of the inorganic powder and granules (A) in the composition, regardless of the form of inclusion, is 170 to 270 parts by mass, and a total content of the inorganic powder and granules (B), regardless of the form of inclusion, is 5 to 50 parts by mass.
[2] The dental curable composition according to the above [1], wherein in each aggregate particle (c) constituting the inorganic powder/granule (C), the inorganic particles (b) are uniformly dispersed in the inorganic particles (a).
[3] The dental hardenable composition according to the above [1] or [2], wherein the inorganic particles (a) are made of a silica-based inorganic compound, and the inorganic particles (b) are made of a crystalline rare earth metal fluoride.
[4] The dental curable composition according to any one of [1] to [3] above, wherein the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained by X-ray diffraction measurement of the inorganic powder/grain (B) is 0.3° or more.
[5] The dental curable composition according to any one of [1] to [4] above, wherein the inorganic powder (C) is obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium to obtain a uniform mixed slurry, and spray-drying the mixture.
[6] A method for producing the dental curable composition according to any one of the above [1] to [5], comprising mixing the polymerizable monomer (M), the inorganic powder/particles (C), and at least one of the inorganic powder/particles (A) and the organic-inorganic composite powder/particles (D).
[7] The method for producing the dental curable composition according to the above item [6], wherein the inorganic powder (C) is produced by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium, to obtain a uniform mixed slurry, and spray-drying the resulting mixture.
[8] The method for producing a dental hardenable composition according to the above [7], wherein the mixed slurry does not contain an ionic surfactant.
[9] The method for producing a dental hardenable composition according to the above [7] or [8], wherein the concentration of the mixed slurry is less than 40 mass%.
[10] An inorganic powder/granule (C) comprising agglomerated particles (c) including a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential when measured in water, and an average primary particle diameter measured by an electron microscope of 50 nm to 1 μm, and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, and an inorganic powder/granule (B) comprising agglomerated particles (c) including agglomerated particles (c) including a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, and an average primary particle diameter measured by an electron microscope of 1 to 300 nm,
the average value of the total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) contained in each of the aggregate particles (c) constituting the inorganic powder or granule (C) is within a range of 20 to 300 parts by mass;
An inorganic powder or granule having an average agglomerated particle size, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method, of 1 to 50 μm, and containing no ionic surfactant.
[11] A method for producing an inorganic powder or granule according to the above item [10], comprising a step of spray-drying a uniform mixed slurry obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder or granule (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder or granule (B) is dispersed in a dispersion medium, wherein the mixed slurry does not contain an ionic surfactant.
[12] The method for producing inorganic powder or granular material according to the above [11], wherein the concentration of the mixed slurry is less than 40 mass%.

According to the present invention, it is possible to provide a dental hardenable composition which has high dispersibility of inorganic powder particles in the composition, good dischargeability from a syringe, appropriate fluidity with little change in the fluidity over time, and high mechanical strength after hardening.
Furthermore, according to the present invention, it is possible to provide inorganic powders and particles which have good dispersibility when blended in a dental hardenable composition, and a method for producing the same.

FIG. 1 is a schematic diagram showing inorganic powder particles (A) to (C) according to the present invention. 1 is an image of the cured product of the dental hardenable composition of Example 1 observed with a scanning electron microscope. 1 is an image of a cured product of the dental hardenable composition of Comparative Example 8, observed with a scanning electron microscope.

[Dental curable composition]
The dental curable composition of the present invention contains inorganic powder particles (C) composed of a polymerizable monomer (M) and aggregate particles (c). Furthermore, the dental curable composition of the present invention contains at least one of inorganic powder particles (A) and organic-inorganic composite powder particles (D) as a powder particle other than the inorganic powder particles (C). Here, the aggregate particles (c) are aggregate particles composed of inorganic particles (a) constituting the inorganic powder particles (A) and inorganic particles (b) constituting the inorganic powder particles (B). Therefore, the dental curable composition of the present invention can contain the inorganic powder particles (A) and the inorganic powder particles (B) in a specific form, specifically, (A) in the form of (C) and in the form of (A) itself or (D) and (B) in the form of (C).
Each component of the dental hardenable composition of the present invention will be described in detail below.

In this specification, unless otherwise specified, the notation "x~y" using the numerical values x and y means "greater than or equal to x and less than or equal to y." In such notations, when a unit is assigned only to the numerical value y, the unit is also applied to the numerical value x. In addition, in this specification, the term "(meth)acrylic" means both "acrylic" and "methacrylic." Similarly, the term "(meth)acrylate" means both "acrylate" and "methacrylate," and the term "(meth)acryloyl" means both "acryloyl" and "methacryloyl."

<Polymerizable monomer (M)>
The dental curable composition of the present invention contains a polymerizable monomer. As the polymerizable monomer, any polymerizable monomer such as a radical polymerizable monomer or a cationic polymerizable monomer used in conventional dental curable compositions can be used without any particular limitation. Among them, it is preferable to use a (meth)acrylate-based polymerizable monomer that is widely used, specifically an acidic group-containing (meth)acrylate-based polymerizable monomer, a hydroxyl group-containing (meth)acrylate-based polymerizable monomer, or a monofunctional or polyfunctional (meth)acrylate-based polymerizable monomer that does not have any of these substituents.

Examples of (meth)acrylate-based polymerizable monomers that can be suitably used include the following. That is, examples of acidic group-containing (meth)acrylate-based polymerizable monomers include (meth)acrylic acid, N-(meth)acryloyl-p-aminobenzoic acid, 2-(meth)acryloyloxybenzoic acid, 2-(meth)acryloyloxyethylphenylhydrogenphosphate, and 2-(meth)acryloyloxyethylphosphonic acid. Examples of hydroxyl group-containing (meth)acrylate-based polymerizable monomers include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 2,2-bis[(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane, and 2,2-bis[4-(4-methacryloyloxy)-3-hydroxybutoxyphenyl]propane. Furthermore, examples of monofunctional and polyfunctional (meth)acrylate polymerizable monomers not having the above-mentioned substituents include methyl (meth)acrylate, ethyl (meth)acrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,6-bis(methacrylethyloxycarbonylamino)trimethylhexane, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane, etc.

Among these polymerizable monomers, bifunctional or higher polymerizable monomers, and more preferably bifunctional to tetrafunctional polymerizable monomers, are preferred because of their high polymerizability and the particularly high mechanical strength of the cured body. These polymerizable monomers may be used alone or in combination with different types.

<Inorganic powder (C)>
The inorganic powder granules (C) contained in the dental curable composition of the present invention are inorganic powder granules (C) composed of agglomerated particles (c) consisting of a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential when measured in water, constituting inorganic powder granules (A) having an average primary particle diameter of 50 nm to 1 μm when measured by an electron microscope, and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, constituting inorganic powder granules (B) having an average primary particle diameter of 1 to 300 nm when measured by an electron microscope.
The average value of the total mass of the inorganic particles (b) per 100 parts by mass of the total mass of the inorganic particles (a) contained in each of the agglomerated particles (c) constituting the inorganic powder or granule (C) is within a range of 20 to 300 parts by mass, and the average agglomerated particle diameter, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method, is 1 to 50 μm.
Each component constituting the inorganic powder (C) will be described in detail below.

The inorganic powder particles (A) contained as the inorganic powder particles (C) in the dental curable composition of the present invention are composed of a plurality of inorganic particles (a), as shown typically in Fig. 1. The inorganic powder particles (A) are an aggregate of the inorganic particles (a) which are primary particles.
In addition, the inorganic powder/granule (A) composed of a plurality of inorganic particles (a) exhibits a zeta potential with a negative polarity when measured in water, and the plurality of inorganic particles (a) are composed of the same type of material. Note that "composed of the same type of material" means that the plurality of inorganic particles (a) constituting the inorganic powder/granule (A) have the same chemical structure.

The inorganic powder particles (B) contained as the inorganic powder particles (C) in the dental curable composition of the present invention are composed of a plurality of inorganic particles (b), as shown typically in Fig. 1. The inorganic powder particles (B) are an aggregate of the inorganic particles (b) which are primary particles.
In addition, the inorganic powder/granule (B) composed of a plurality of inorganic particles (b) exhibits a positive zeta potential when measured in water, and the inorganic particles (b) are composed of the same material. Note that "composed of the same material" means that the inorganic particles (b) constituting the inorganic powder/granule (B) have the same chemical structure.
Here, the polarity of the zeta potential measured in water means the polarity (sign, i.e., positive or negative) of the zeta potential measured by electrophoretic light scattering for inorganic powder or granules dispersed in ion-exchanged water of pH 7.

The inorganic powder (C) is composed of aggregate particles (c) consisting of inorganic particles (a) constituting the inorganic powder (A) and inorganic particles (b) constituting the inorganic powder (B), as shown in Fig. 1. The aggregate particles (c) are composed of a plurality of inorganic particles (a) and a plurality of inorganic particles (b), and any inorganic particle constituting the aggregate particles is in contact with any other inorganic particle constituting the aggregate particles. The formation of the aggregate particles (c) can be confirmed by an electron microscope.
The inorganic powder or particle (C) is an aggregate of a plurality of agglomerated particles (c).
When the inorganic powder (C) is blended in a dental hardenable composition, the generation of aggregates, particularly the generation of aggregates caused by the inorganic particles (b), is suppressed. For example, when a crystalline rare earth metal fluoride is used as the inorganic particles (b), aggregates of the crystalline rare earth metal fluoride are generally likely to be generated, but when the inorganic powder (C) is blended in a dental hardenable composition, the generation of aggregates is suppressed. Therefore, the dental hardenable composition of the present invention has good dispersibility of the inorganic powder and can reduce the change in flowability over time.
The reason for this is unclear, but is presumed to be as follows. That is, the inorganic powder (C) is composed of aggregated particles (c), and the inorganic particles (b) such as crystalline rare earth metal fluoride and the inorganic particles (a) such as silica-based inorganic compounds are dispersed and mixed at the primary particle level, so that the generation of aggregates of the inorganic particles (b) such as crystalline rare earth metal fluoride is suppressed, and the dispersibility is improved. And, it is considered that the generation of aggregates of the inorganic particles (b) such as crystalline rare earth metal fluoride is suppressed in this way, and thus the change in the fluidity of the dental hardenable composition over time can be reduced.

Furthermore, the inorganic powder (C) can be produced, for example, by spray-drying a mixed slurry containing the inorganic powder (A) and the inorganic powder (B), as described below. Since the inorganic powder (C) can suppress an increase in the viscosity of the slurry used during production, it is easy to produce the inorganic powder (C) by spray-drying.
The reason for this is unclear, but is presumed to be as follows.
That is, as described above, inorganic particles (a) show a negative zeta potential in water, while inorganic particles (b) show a positive zeta potential in water. In the present invention, the average primary particle size of each of the inorganic powder (A) composed of inorganic particles (a) and the inorganic powder (B) composed of inorganic particles (b) is set to a specific range, and the content of the inorganic particles (b) relative to the inorganic particles (a) is set to a specific range. Therefore, in the slurry used for spray drying, a unit is formed in which the inorganic particles (a) showing a negative zeta potential are covered with the inorganic particles (b) showing a positive zeta potential, and the units repel each other due to the positive charge, so that the increase in viscosity is suppressed.
The composition of the inorganic powder (C) will be described in more detail below. First, inorganic powder (A) and inorganic powder (B) which are part of the inorganic powder (C) and are used as raw materials for producing the inorganic powder (C) will be described.

The inorganic powder or granule (A) in the present invention is composed of a plurality of inorganic particles (a).
The inorganic powder or granule (A) has an average primary particle diameter of 50 nm to 1 μm. The average primary particle diameter is measured using a scanning or transmission electron microscope as follows. That is, n inorganic primary particles (a), which are 30 or more, preferably 100 or more, randomly selected from electron microscope images in which light and dark are clearly distinguishable and particle contours can be distinguished, are subjected to image analysis to determine the circle equivalent diameter (diameter of a circle having the same area as the area of the target particle): _Xi of each inorganic particle (a), and the average particle (volume) diameter: X calculated from the sum of X _i ³ from the 1st particle to the nth particle: ΣX _i ³ according to the formula: X = {(ΣX _i ³ )/n} ^1/3 .

By setting the average primary particle diameter of the inorganic powder (A) to 50 nm to 1 μm and the average primary particle diameter of the inorganic powder (B) and the mass ratio of the inorganic particles (a) and the inorganic particles (b) contained in the aggregate particles (c) to specific ranges as described below, it becomes easier to adjust the viscosity of the slurry low during the production of the inorganic powder (C). Therefore, when the average primary particle diameter of the inorganic powder (A) is 50 nm to 1 μm, it becomes easier to obtain the inorganic powder (C) by the spray drying method. From this viewpoint and from the viewpoint of improving the polishability of the cured product when it is blended into a dental curable composition, the average primary particle diameter of the inorganic powder (A) is preferably 0.15 to 1.0 μm, and more preferably 0.15 to 0.8 μm.

The shape of the inorganic particles (a) constituting the inorganic powder (A) is not particularly limited, and spherical, approximately spherical, or irregularly shaped particles can be used, but from the viewpoint of excellent wear resistance and surface smoothness of the cured product of the dental curable composition, it is preferable that the inorganic particles (a) are spherical or approximately spherical. Note that, the approximately spherical shape refers to an average uniformity Pr of 0.6 or more, which is defined by the formula: Pr = (ΣB i /L i ) / n based on the ratio of the maximum length of each particle, _Li , to the minimum width, Bi _, which is the diameter in the direction perpendicular to the major axis, B _i / _Li, which is calculated by image analysis of the inorganic particles ( _a ) selected from the photographed image used when measuring the average particle size, from the _{first particle to the nth particle, ΣB i / Li} . The average uniformity is preferably 0.7 or more, and particularly preferably 0.8 or more. The upper limit of the average uniformity is 1.

The material of the inorganic particles (a) constituting the inorganic powder and granules (A) is not particularly limited as long as the polarity of the zeta potential is negative, and examples of materials that can be used include metal oxides such as amorphous silica, quartz, titania, zirconia, chromium oxide, iron oxide, and tungsten oxide, which are used as fillers in conventional dental hardenable compositions; and composite oxides such as silica-zirconia, silica-titania, silica-titania-barium oxide, silica-titania-zirconia, borosilicate glass, aluminosilicate glass, and fluoroaluminosilicate glass.
The material of the inorganic particles (a) is preferably a silica-based inorganic compound because it is widely used and easily available. A silica-based inorganic compound means an inorganic compound containing silica. Among silica-based inorganic compounds, it is particularly preferable to use those made of silica-based composite oxides such as the above-mentioned silica-zirconia, silica-titania, silica-titania-barium oxide, and silica-titania-zirconia, and silica-zirconia is more preferable. Many silica-based composite oxide particles have strong acid sites on the surface, and the degree of negativity of the zeta potential is often large.
The zeta potential of the inorganic powder (A) in water is preferably −20 mV or less, more preferably −40 mV or less. The lower limit of the zeta potential is not particularly limited, but is generally −100 mV or more. The inorganic powder (A) may be a combination of a plurality of inorganic powders having different average primary particle sizes, and in that case, the zeta potential of each of the plurality of inorganic powders is preferably within the above-mentioned range.
The inorganic powder or particle (A) may be surface-treated with a silane coupling agent or the like, so long as the polarity of the zeta potential is not changed.

The inorganic powder (B) in the present invention is composed of a plurality of inorganic particles (b).
The inorganic powder (B) has an average primary particle size of 1 to 300 nm. By setting the range of the average primary particle size of the inorganic powder (B) and the average primary particle size of the inorganic powder (A) and the amount of each inorganic powder within a specific range, it becomes easy to reduce the viscosity of the slurry used in producing the inorganic powder (C) of the present invention. Furthermore, as described below, when producing the inorganic powder (B) by mechanochemical treatment, those with an average primary particle size of less than 1 nm are not preferred because they require a long treatment time.
In addition, when the average primary particle size of the inorganic powder and particles (B) is 1 to 300 nm, the polishability and transparency of the cured product of the dental curable composition can be easily improved.
From the viewpoint of decreasing the slurry viscosity and improving the polishability and transparency of the cured body of the dental curable composition, the average primary particle size of the inorganic powder and particle (B) is preferably 15 to 280 nm, and more preferably 15 to 200 nm.
The average primary particle size of the inorganic powder or particles (B) can be measured by the same method as the above-mentioned method for measuring the average primary particle size of the inorganic powder or particles (A).

The zeta potential of the inorganic powder or granule (B) is positive. The zeta potential of the inorganic powder or granule (B) is preferably 10 mV or more, preferably 20 mV or more, and preferably 60 mV or less.

As the material of inorganic particle (b), rare earth metal compound particles are preferred from the viewpoint of color tone and safety.Among them, it is preferred to use crystalline rare earth metal fluorides such as ytterbium fluoride (YbF ₃ ), lanthanum fluoride (LaF ₃ ), cerium fluoride (CeF ₃ ), gadolinium fluoride (GdF ₃ ), etc., and from the viewpoint of X-ray opacity, it is most preferred to use ytterbium fluoride.It should be noted that whether or not it is crystalline can be judged by whether or not the peak based on crystal plane is confirmed when performing X-ray diffraction measurement.

In the present invention, when the inorganic powder (B) composed of a crystalline rare earth metal fluoride is used, it is preferable that the specific surface area is increased by pulverization or the like. By increasing the specific surface area, the formability of the dental hardenable composition, which is a paste, is improved. Here, formability means the property of not deforming after the dental hardenable composition is discharged from a syringe until it is hardened (the property of not deforming easily due to natural flow when left to stand, and being able to maintain its shape).
The specific surface area of the inorganic powder (B) is preferably 10 to 100 ^{m 2} /g, more preferably 10 to 80 m ² /g, and further preferably 10 to 70 m ² /g. The specific surface area can be measured by a nitrogen adsorption method.

As a method for increasing the specific surface area of the inorganic powder (B), there may be mentioned a method for pulverizing the raw material powder (B') of the inorganic powder (B).
The pulverization method is not particularly limited, but mechanochemical treatment is preferred because it suppresses the decrease in transparency when mixed into a dental hardenable composition and makes it easy to adjust the transparency to an appropriate level for a composite resin. By using the mechanochemical treatment, it is possible to obtain a rare earth metal fluoride having an increased specific surface area and an increased amorphousness.

Ytterbium fluoride ( _YbF3 ) is well known as an X-ray contrast filler, but when it is mixed into dental hardenable compositions such as composite resins, it is known that the transparency of the hardened body decreases. The decrease in transparency can be suppressed by increasing the amorphousness by mechanochemical treatment.

The mechanochemical treatment means a treatment in which mechanical energy is applied to the raw material powder, and means a treatment in which at least one of mechanical grinding, pulverization, and dispersion is performed. In order to reliably and efficiently increase the specific surface area of the inorganic powder or grain (B), it is preferable to adopt a wet method, and it is particularly preferable to perform a treatment using a wet bead mill (wet bead mill treatment).
The wet bead mill treatment will be described in detail later.

Mechanochemical treatment conditions vary depending on the operating method of the wet bead mill used, the bead diameter, the type of inorganic powder, the slurry concentration, and other conditions. These conditions can be adjusted by conducting preliminary experiments using the equipment and conditions that will actually be used for mechanochemical treatment, and then confirming the specific surface area of the treated inorganic powder versus the mechanochemical treatment time.

When the inorganic powder (B) composed of a crystalline rare earth metal fluoride is mechanochemically treated, in addition to the aforementioned effect of increasing the specific surface area, the crystallinity of the crystalline rare earth metal fluoride is reduced, suppressing the decrease in transparency when it is mixed into a dental hardenable composition, and making it easier to adjust the transparency to an appropriate level for a composite resin.

When an inorganic powder (B) composed of a crystalline rare earth metal fluoride is used, it is preferable that the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained by performing X-ray diffraction measurement on the inorganic powder (B) is 0.3° or more.
The crystallinity of the crystalline rare earth metal fluoride can be evaluated by the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern, and the smaller the full width at half maximum, the higher the crystallinity. Incidentally, the full width at half maximum of the maximum intensity peak of the rare earth metal fluoride generally used as an X-ray opaque material or the commercially available rare earth metal fluoride powder available as a raw material powder is usually less than 0.3° (specifically, about 0.12° to 0.27°), and when such a rare earth metal fluoride powder is blended, the transparency decreases. In order to obtain the effect of suppressing the decrease in the transparency, it is necessary to make the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern 0.3° or more by, for example, performing a mechanochemical treatment, and from the viewpoint of the effect of suppressing the decrease in transparency, it is preferable that the full width at half maximum of the maximum intensity peak is 0.4° or more, particularly 0.5° or more.
The full width at half maximum of the maximum intensity peak increases as the mechanochemical treatment time is increased, but the amount of increase varies depending on various conditions, so it is preferable to carry out a preliminary experiment based on the device and conditions for carrying out the mechanochemical treatment and confirm the full width at half maximum derived from the crystalline rare earth metal fluoride with respect to the mechanochemical treatment time. The upper limit of the full width at half maximum is not particularly limited, but in the case of mechanochemical treatment, it usually does not exceed 2.0°.

The full width at half maximum of the maximum intensity peak in the X-ray diffraction pattern can be determined by performing X-ray diffraction measurement on the inorganic powder (B) composed of the crystalline rare earth metal fluoride in the present invention. Specifically, an X-ray diffraction measurement is performed with an X-ray diffractometer in the range of 2θ; 20 to 120°, and the peaks derived from the crystalline rare earth metal fluoride in the obtained X-ray diffraction pattern (chart) with the horizontal axis being 2θ (°) and the vertical axis being diffraction intensity are identified, and the full width at half maximum of the peak having the maximum intensity (for example, for YbF ₃ , the peak corresponding to the crystal plane (1,1,1) that appears near 2θ = 28.0°) is obtained, that is, the peak width at the intensity where the intensity is 50% of the peak intensity (maximum intensity) (the absolute value of the difference between the 2θ of the two intersections between the intensity and the peak line: unit "(°)") can be determined. In addition, when measuring, it is preferable to use a powder from which coarse particles have been removed, for example, by using a sieve with an opening of 100 μm, as the measurement sample.

As described above, the inorganic powder (C) used in the present invention is composed of aggregate particles (c) consisting of the inorganic particles (a) constituting the inorganic powder (A) and the inorganic particles (b) constituting the inorganic powder (B).

The average value of the total mass of the inorganic particles (b) per 100 parts by mass of the total mass of the inorganic particles (a) contained in each of the agglomerated particles (c) constituting the inorganic powder or granule (C) is within a range of 20 to 300 parts by mass.
When the average value of the total mass of the inorganic particles (b) exceeds 300 parts by mass relative to 100 parts by mass of the total mass of the inorganic particles (a), when the inorganic powder (C) is blended into the dental curable composition, dispersibility becomes poor and agglomerates are likely to occur.
On the other hand, when the average value of the total mass of the inorganic particles (b) relative to 100 parts by mass of the total mass of the inorganic particles (a) is less than 20 parts by mass, it becomes difficult to produce the inorganic powder (C) by a spray drying method. Even if the inorganic powder (C) can be produced, the effect based on the blending of the inorganic particles (b) is likely to decrease, for example, the formability of the dental curable composition is likely to decrease, and when the inorganic particles (b) are X-ray opaque, the X-ray contrast property is likely to decrease.
The average value of the total mass of the inorganic particles (b) per 100 parts by mass of the total mass of the inorganic particles (a) contained in each of the aggregate particles (c) is preferably 22 to 280 parts by mass, and more preferably 25 to 250 parts by mass.
The total mass of the inorganic particles (b) relative to 100 parts by mass of the inorganic particles (a) can be adjusted by the amounts of the inorganic powder (A) and the inorganic powder (B) used when producing the inorganic powder (C). That is, when producing the inorganic powder (C) by the spray drying method described later, the total mass of the inorganic particles (b) can be adjusted by the ratio of the amounts of the inorganic powder (A) and the inorganic powder (B) contained in the mixed slurry to be spray dried.

As described above, the inorganic powder (C) is an aggregate of a plurality of agglomerated particles (c) having different particle sizes.
The inorganic powder or granule (C) has an average agglomerated particle size (i.e., the average particle size of a plurality of agglomerated particles (c)) of 1 to 50 μm. Inorganic powder or granule (C) having such an average agglomerated particle size is easy to handle. Inorganic powder or granules having an average agglomerated particle size of less than 1 μm or an average agglomerated particle size of more than 50 μm are difficult to prepare.
The average agglomerated particle size of the inorganic powder or particles (C) is preferably 3 to 30 μm, more preferably 5 to 25 μm, from the viewpoint of improving handleability.
The average agglomerated particle size of the inorganic powder (C) can be adjusted to a desired range by adjusting the production conditions, such as the amount of the dispersion medium used, in the spray drying method described below.
The average agglomerated particle size of the inorganic powder or particles (C) can be measured by a laser diffraction-scattering method.

The inorganic powder (C) preferably does not contain an ionic surfactant. When the inorganic powder (C) does not contain an ionic surfactant, it does not cause the inhibition of curing caused by the ionic surfactant, the discoloration caused by the adsorption of the pigment to the ionic surfactant, or the decrease in strength caused by the elution of the ionic surfactant when it is blended into a dental curable composition.

<Method for producing inorganic powder (C)>
The method for producing the inorganic powder (C) is not particularly limited, but it is preferable to produce it by a spray drying method using a mixed slurry containing the inorganic powder (A) and the inorganic powder (B) described above. This will be explained in detail below.

The inorganic powder (C) can be obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium, and then spray-drying the resulting uniform mixed slurry.
By such a production method including a spray drying step, an inorganic powder (C) composed of agglomerated particles (c) in which inorganic particles (b) are uniformly dispersed in inorganic particles (a) can be obtained. Here, "uniformly dispersed" means a state in which inorganic particles (a) and inorganic particles (b) are dispersed and mixed at the primary particle level in the agglomerated particles (c), and when the inorganic powder (C) is observed with an electron microscope, for example, the brightness of each constituent particle (c) is uniform, and particles having a specifically high brightness region or particles with an overall high brightness such as agglomerated particles composed only of inorganic particles (b) are not observed.

The mixed slurry is obtained by going through a process of preparing a slurry (Sa) and a process of preparing a slurry (Sb), and then mixing the slurry (Sa) and the slurry (Sb).

The step of preparing the slurry (Sa) is preferably carried out by dispersing the slurry obtained by mixing the dispersion medium and the inorganic powder (A). As the dispersion medium, water is preferably used, but water to which an organic solvent is added as necessary may also be used. Examples of the organic solvent include ethanol, isopropyl alcohol, chloroform, and dimethylformamide.
The amount of the dispersion medium used is usually 40 to 900 parts by mass per 100 parts by mass of the inorganic powder or particles (A).
The dispersion treatment can be carried out using a mixer such as a bead mill.

As the inorganic particles (a) constituting the inorganic powder (A) contained in the slurry (Sa), a silica-based inorganic compound is preferred because it is widely used and easily available. Therefore, the slurry (Sa) is preferably a slurry in which inorganic particles (a) made of a silica-based inorganic compound are dispersed in water.
Among the above silica-based inorganic compounds, silica-based composite oxides such as silica-zirconia, silica-titania, silica-titania-barium oxide, and silica-titania-zirconia are particularly preferred.

The step of preparing the slurry (Sb) is preferably carried out by dispersing a slurry containing a dispersion medium and an inorganic powder (B). As the dispersion medium, water is preferably used, but water to which an organic solvent is added as necessary may also be used. Examples of the organic solvent include ethanol, isopropyl alcohol, chloroform, and dimethylformamide.
The amount of the dispersion medium used is usually 40 to 900 parts by mass per 100 parts by mass of the inorganic powder or particles (B).
The dispersion treatment can be carried out using a mixer such as a bead mill.

The inorganic particles (b) constituting the inorganic powder and granules (B) contained in the slurry (Sb) are preferably crystalline rare earth metal fluorides from the viewpoints of color tone, stability, etc. Therefore, the slurry (Sb) is preferably a slurry in which inorganic particles (b) made of crystalline rare earth metal fluoride are dispersed in water.
Among the above crystalline rare earth metal fluorides, ytterbium fluoride (YbF ₃ ), lanthanum fluoride (LaF ₃ ), cerium fluoride (CeF ₃ ), gadolinium fluoride (GdF ₃ ), etc. are preferred, and from the viewpoint of X-ray opacity, it is most preferred to use ytterbium fluoride.

When inorganic powder (B) composed of crystalline rare earth metal fluoride is used, it is preferable to subject raw powder (B') to wet bead milling using water as a medium (dispersion medium) in the step of preparing slurry (Sb). The raw powder (B') is composed of crystalline rare earth metal fluoride particles, and the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained by X-ray diffraction measurement is less than 0.3°.
By subjecting the raw powder particles (B') to a wet bead mill treatment, it is possible to obtain the slurry (Sb) in which the inorganic powder particles (B) are dispersed, the full width at half maximum of the maximum intensity peak derived from a crystalline rare earth metal fluoride being 0.3° or more in an X-ray diffraction pattern obtained by X-ray diffraction measurement.
The inorganic powder of the present invention produced using such a slurry (Sb) in which the inorganic powder (B) is dispersed suppresses the decrease in transparency when blended with a dental hardenable composition, and makes it easy to adjust the transparency to an appropriate level for a composite resin.

Wet bead mill processing is a mechanochemical process in which a slurry of the powder to be processed and a medium (dispersion medium) is brought into contact with media (beads) that have been stirred, vibrated, or otherwise imparted movement to the powder, thereby crushing and disintegrating the powder. Materials used as media include glass, alumina, zircon, zirconia, steel, and resin, but it is preferable to use beads made of alumina or zirconia because of their excellent abrasion resistance and relatively low contamination. The size of the beads used can be selected according to the average particle size of the desired inorganic powder (B), and there are no particular restrictions, but it is preferable to use beads with a diameter of 0.01 to 0.5 mm in order to obtain inorganic powder (B) that is suitable for incorporation into dental hardenable compositions.

Depending on the operating method, wet bead mills come in a variety of types, including a batch type in which the slurry and beads are directly fed into the equipment for processing, a circulation type in which the slurry is circulated between a tank and the equipment, and a pass type in which the slurry is passed through the equipment a specified number of times. The operating method can be selected based on the amount of raw powder (B') used for processing. It is preferable to use a circulation type bead mill or a pass type bead mill, as they are highly productive and can process relatively large amounts of inorganic powder.

Depending on the operating method, such as the circulation type or pass type, it is necessary to separate the slurry and beads when carrying out the mechanochemical treatment. Examples of bead separation methods include slit type, screen type, and centrifugal separation type, and these bead separation methods can be selected according to the particle size of the beads used, and any method can be used without particular restrictions. The concentration of the slurry used in the mechanochemical treatment is usually 40 to 900 parts by mass of dispersion medium per 100 parts by mass of raw powder (B').

For every 100 parts by mass of inorganic powder (A) contained in the slurry (Sa), the inorganic powder (B) contained in the slurry (Sb) is preferably 20 to 300 parts by mass, more preferably 22 to 280 parts by mass, and even more preferably 25 to 250 parts by mass.

The slurry (Sa) and the slurry (Sb) prepared as described above are mixed to obtain a uniform mixed slurry. The mixing can be performed using a stirrer or the like.
The mixed slurry preferably does not contain an ionic surfactant. In the present invention, the viscosity of the mixed slurry can be reduced without using an ionic surfactant, and the slurry becomes suitable for spray drying, which will be described later.
In addition, since the mixed slurry does not contain an ionic surfactant, an inorganic powder (C) that does not contain an ionic surfactant can be obtained. When such an inorganic powder (C) that does not contain an ionic surfactant is mixed into a dental curable composition, the curing inhibition caused by the ionic surfactant, discoloration caused by the adsorption of a dye to the ionic surfactant, and further, a decrease in strength caused by the elution of the ionic surfactant do not occur.
Examples of the ionic surfactant include anionic surfactants, cationic surfactants, and amphoteric surfactants.
A surfactant is a compound that has a hydrophilic group and a hydrophobic group in one molecule. An anionic surfactant is a surfactant that can become an ion in an aqueous solution and the hydrophilic group becomes an anion. A cationic surfactant is a surfactant that can become an ion in an aqueous solution and the hydrophilic group becomes a cation. An amphoteric surfactant is a compound that, when dissolved in water, exhibits the properties of an anionic surfactant in the alkaline range and the properties of a cationic surfactant in the acidic range.

The mixed slurry may contain a surface treatment agent, if necessary. By using the surface treatment agent, the inorganic particles constituting the inorganic powder/particles (A) or the inorganic powder/particles (B) can be surface-treated.
Examples of such surface treatment agents include silane coupling agents such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloyloxypropyltrimethoxysilane, κ-methacryloyloxydodecyltrimethoxysilane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, γ-glycidoxypropyl-trimethoxysilane, N-β-(aminoethyl)-γ-aminopropyl-trimethoxysilane, γ-ureidopropyl-triethoxysilane, γ-chloropropyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, and methyltriethoxysilane, and titanate-based coupling agents.
The amount of the surface treatment agent to be added is, for example, 0.1 to 10 parts by mass, and preferably 0.5 to 5 parts by mass, per 100 parts by mass of the total of the inorganic powder particles (A) and the inorganic powder particles (B).

The mixed slurry is spray-dried to obtain the inorganic powder (C).
The spray drying method may be a method in which the mixed slurry is turned into fine droplets using a high-speed air stream, sprayed, and dried (also called a nozzle-type spray drying method), or a method in which the mixed slurry is dropped onto a disk-shaped rotor rotating at a rotation speed of 1000 to 50000 rpm, and then blown off into a mist by centrifugal force to dry (also called a disk-type spray drying method). The inorganic powder (C) obtained is composed of agglomerated particles (c), and from the viewpoint of obtaining agglomerated particles (c) having a uniform particle size, a disk-type spray drying method in which the mist-like mixed slurry is immediately dried with high-temperature air or an inert gas is preferred, and the temperature of the gas used for drying in this case is preferably 60 to 300°C, particularly 80 to 250°C.
Furthermore, the disk type spray drying method allows suitable spray drying even when the mixed slurry has a relatively high concentration.

The concentration of the mixed slurry used in the spray drying is preferably less than 40 mass%, more preferably 38 mass% or less, and even more preferably 35 mass% or less, from the viewpoint of enabling proper spray drying and obtaining desired agglomerated particles, and is preferably 10 mass% or more, from the viewpoint of improving the productivity of the inorganic powdery or granular material (C).
The concentration of the mixed slurry means the concentration (mass %) of the inorganic powder or granule in the mixed slurry.

The inorganic powder (C) obtained by spray drying is preferably subjected to vacuum drying after spray drying from the viewpoint of removing the remaining dispersion medium, etc. Vacuum drying is generally performed under a reduced pressure of 0.01 to 100 hectopascals at 20 to 150° C. for 1 to 48 hours.
The inorganic powder obtained by spray drying may be pulverized as necessary to adjust the average particle size to an appropriate value. As a pulverizing means, a vibration ball mill, a bead mill, a jet mill, or the like can be used.

<Inorganic powder (A), organic-inorganic composite powder (D)>
From the viewpoint of improving the mechanical strength of the cured product, the dental curable composition of the present invention further contains at least one of inorganic powder particles (A) and organic-inorganic composite powder particles (D) as a powder particle other than the inorganic powder particles (C) described above.
The details of the structure of the inorganic powder (A) are as described above, and therefore will not be described here.

The organic-inorganic composite powder (D) is composed of a plurality of organic-inorganic composite particles (d). The organic-inorganic composite particles (d) are a composite material of inorganic powder (A) and a resin, in which the content of the inorganic powder (A) in the composite material is 60 to 90 mass%. The content of the inorganic powder (A) in the composite material is preferably 65 to 90 mass%, more preferably 70 to 90 mass%.
When the organic-inorganic composite powder (D) is used, the inorganic powder (A) can be blended in the composition as the organic-inorganic composite powder (D). Since the inorganic powder (A) in the organic-inorganic composite powder (D) is coated with a resin, it tends to be less likely to interact with the inorganic powder (B).

The resin in the composite material is not particularly limited, but is preferably a cured product obtained by polymerizing a polymerizable monomer. As the polymerizable monomer, those described above as the polymerizable monomer (M) can be used without any particular restrictions.

The organic-inorganic composite powder (D) has an average particle size of 1 to 100 μm. If the average particle size is less than 1 μm, the dental curable composition is poorly ejected from a syringe. If the average particle size is more than 100 μm, the mechanical strength, such as bending strength, of the dental curable composition is likely to decrease.
The average particle size of the organic-inorganic composite powder or particle (D) corresponds to the average value of the particle sizes of a plurality of organic-inorganic composite particles (d), and is an average particle size defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method.

The organic-inorganic composite powder (D) may be obtained by polymerizing a mixture of the inorganic powder (A), a polymerizable monomer, and a polymerization initiator, followed by pulverization. Alternatively, the organic-inorganic composite powder (D) may be a microporous organic-inorganic composite powder obtained by immersing an aggregated powder constituted by inorganic aggregated particles formed by agglomeration of the inorganic particles (a) constituting the inorganic powder (A) in a polymerizable monomer solution containing a polymerizable monomer, a polymerization initiator, and an organic solvent, removing the organic solvent, and then polymerizing and curing the polymerizable monomer. The aggregated powder can be obtained, for example, by spray-drying an aqueous dispersion containing the inorganic powder (A).
As the polymerizable monomer, those described above as the polymerizable monomer (M) can be used without particular limitation, and as the polymerization initiator, those described below as those that may be added to the dental curable composition can be used without particular limitation.

<Contents of inorganic powder and granule (A) and inorganic powder and granule (B) regardless of the form of inclusion>
As described above, the inorganic powder (C) is composed of a plurality of aggregated particles (c), the organic-inorganic composite powder (D) is composed of a plurality of organic-inorganic composite particles (d), and the inorganic powder (A) is composed of a plurality of inorganic particles (a). On the other hand, when producing the inorganic powder (C) and the organic-inorganic composite powder (D), the inorganic powder (A) is used as a raw material as described above, so that the inorganic powder (C) and the organic-inorganic composite powder (D) each contain the inorganic powder (A). Therefore, when the inorganic powder (A) is blended as a powder other than the inorganic powder (C) and the organic-inorganic composite powder (D), the dental curable composition contains the inorganic powder (A) having a different content form. For this reason, the term "total content regardless of the form of inclusion of inorganic powder particles (A)" is used to represent the content of all inorganic powder particles (A) in the dental curable composition (i.e., the total amount of inorganic powder particles (A) including the amount of inorganic powder particles (A) contained in inorganic powder particles (C) and the amount of inorganic powder particles (A) contained in organic-inorganic composite powder particles (D) that is blended as necessary).

In the dental hardenable composition, the total content of the inorganic powder and granules (A), regardless of their content form, is 170 to 270 parts by mass, and more preferably 180 to 250 parts by mass, per 100 parts by mass of the polymerizable monomer (M). If the total content of the inorganic powder and granules (A), regardless of their content form, is less than 170 parts by mass, the dental hardenable composition is likely to experience significant changes in fluidity over time, and the mechanical strength of the hardened product is likely to decrease. If the total content of the inorganic powder and granules (A), regardless of their content form, exceeds 270 parts by mass, the ejection properties become poor.

In addition, when producing inorganic powder (C), inorganic powder (B) is used as a raw material, so inorganic powder (C) contains inorganic powder (B). The dental curable composition of the present invention may contain inorganic powder (B) as a powder other than inorganic powder (C). In such a case, inorganic powder (B) having a different content form is present in the dental curable composition. For this reason, the term "total content of inorganic powder (B) regardless of content form" is used to represent the content of all inorganic powder (B) in the dental curable composition (i.e., the total amount of inorganic powder (B) contained in inorganic powder (C) and the amount of inorganic powder (B) in other content forms that are mixed as necessary).

In the dental curable composition, the total content of the inorganic powder and particle (B), regardless of the form of the powder and particle, is 5 to 50 parts by mass, and preferably 8 to 45 parts by mass, based on 100 parts by mass of the polymerizable monomer (M), from the viewpoint of improving the mechanical strength of the cured product.
If the total content of the inorganic powder (B) is less than 5 parts by mass, regardless of the form of inclusion, the fluidity changes significantly over time, and the formability deteriorates. If the total content of the inorganic powder (B) is more than 50 parts by mass, regardless of the form of inclusion, the ejection property deteriorates.

<Polymerization initiator>
A polymerization initiator may be added to the dental hardenable composition of the present invention. The polymerization initiator is not particularly limited as long as it has a function of polymerizing the polymerizable monomer, but it is preferable to use a photopolymerization initiator or a chemical polymerization initiator used in direct dental filling and restoration applications in which hardening is often performed in the oral cavity, and it is more preferable to use a photopolymerization initiator from the viewpoint of simplicity without the need for a mixing operation.

Polymerization initiators used in photopolymerization include benzoin alkyl ethers such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; benzil ketals such as benzil dimethyl ketal and benzil diethyl ketal; benzophenones such as benzophenone, 4,4'-dimethylbenzophenone, and 4-methacryloxybenzophenone; α-diketones such as diacetyl, 2,3-pentanedione benzyl, camphorquinone, 9,10-phenanthraquinone, and 9,10-anthraquinone; and 2,4-diethoxythioxanthone. Thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, and methylthioxanthone, and bisacylphosphine oxides such as bis-(2,6-dichlorobenzoyl)phenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide, bis-(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide can be used.

In addition, reducing agents are often added to photopolymerization initiators. Examples of reducing agents include tertiary amines such as 2-(dimethylamino)ethyl methacrylate, ethyl 4-dimethylaminobenzoate, and N-methyldiethanolamine; aldehydes such as lauryl aldehyde, dimethylaminobenzaldehyde, and terephthalaldehyde; and sulfur-containing compounds such as 2-mercaptobenzoxazole, 1-decanethiol, thiosalicylic acid, and thiobenzoic acid.

Furthermore, in addition to the above photopolymerization initiator and reducing agent, a photoacid generator is often used. Examples of such photoacid generators include diaryliodonium salt compounds, sulfonium salt compounds, sulfonic acid ester compounds, halomethyl-substituted S-triazine derivatives, and pyridinium salt compounds.

These polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator to be used may be selected from an effective amount depending on the purpose, and is usually used in a ratio of 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the polymerizable monomer.
<Other additives>
The dental hardenable composition of the present invention may contain additives such as polymerization inhibitors, pigments, ultraviolet absorbers, and fluorescent agents, within limits that do not impair the effects of the composition.

The dental curable composition of the present invention can be prepared by mixing at least one of the polymerizable monomer (M), the inorganic powder and granules (C), the inorganic powder and granules (A), and the organic-inorganic composite powder and granules (D), as well as any optional components that are blended as necessary, in predetermined blending amounts to obtain a paste, and further degassing this paste under reduced pressure to remove any air bubbles.
The dental hardenable composition of the present invention has good dischargeability from a syringe, appropriate fluidity, and small change in the fluidity over time, and has high mechanical strength after hardening, so that it can be suitably used as a flowable composite resin.

[Inorganic powder (C)]
In the present invention, when blended in a dental curable composition, the inorganic powder (C) can be provided as an inorganic powder having good dispersibility.
The inorganic powder/granule (C) is an inorganic powder/granule (C) composed of agglomerated particles (c) consisting of a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential polarity when measured in water, constituting inorganic powder/granule (A), and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential polarity when measured in water, constituting inorganic powder/granule (B), and agglomerated particles (c) consisting of the inorganic particles (b) and the inorganic particles (b) and the inorganic powder/granule (B),
the average value of the total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) contained in each of the aggregate particles (c) constituting the inorganic powder or granule (C) is within a range of 20 to 300 parts by mass;
The inorganic powder (C) has an average agglomerated particle size, defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method, of 1 to 50 μm and does not contain an ionic surfactant.
The details of the inorganic powder (C) and the method for producing the same are the same as those of the inorganic powder (C) contained in the dental curable composition described above, and therefore will not be described here.

The present invention will be specifically described below with reference to examples and comparative examples, although the present invention is not limited to these examples.
First, in the examples and comparative examples, the substances used as raw materials for the compositions prepared and their abbreviations, as well as the evaluation methods for the raw materials and the compositions prepared will be described.

1. Raw materials and their abbreviations (1) Polymerizable monomers ・UDMA: 1,6-bis(methacrylethyloxycarbonylamino)-2,2-4-trimethylhexane ・3G: Triethylene glycol dimethacrylate ・GMA: 2,2-bis[(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane ・D-2.6E: 2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane

(2) Inorganic Powder and Particles The average primary particle size and the average uniformity are values determined for each inorganic powder and particle based on the evaluation method described below.
(2)-1 Inorganic powder composed of silica-based inorganic compound ・FA-1: Inorganic powder composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle diameter 150 nm, average uniformity: 0.95)
FA-2: Inorganic powder composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle diameter 260 nm, average uniformity: 0.95)
FA-3: Inorganic powder composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle diameter: 400 nm, average uniformity: 0.9)
FA-4: Inorganic powder composed of amorphous silica-zirconia particles produced by the sol-gel method (average primary particle diameter 1000 nm)
FA-5: Inorganic powder composed of silica (average primary particle size 300 nm, manufactured by Nippon Shokubai Co., Ltd.)
FA-6: Inorganic powder composed of spherical silica-zirconia particles produced by the sol-gel method (average primary particle size: 40 nm, average uniformity: 0.90)
FA-7: Inorganic powder (average primary particle diameter 4000 nm) composed of amorphous silica-zirconia produced by the sol-gel method.

(2)-2 Inorganic powder particles composed of crystalline rare earth fluoride particles: YbF ₃ -40: Inorganic powder particles composed of ytterbium fluoride 3 (average primary particle size 46 nm, manufactured by Treibacer).
YbF ₃ -200: Inorganic powder and granules composed of ytterbium trifluoride (average primary particle size 200 nm, manufactured by Treibacer).
YbF ₃ -300: Inorganic powder and granules composed of ytterbium trifluoride (average primary particle size 270 nm, manufactured by Treibacer).

(3) Polymerization initiator CQ: camphorquinone DMBE: N,N-dimethyl-p-ethyl benzoate.

2. Manufacturing method, evaluation method, and evaluation results of inorganic powders (1) Inorganic powders (A) made of silica-based inorganic compounds The average primary particle size and zeta potential of the inorganic powders FA-1 to FA-7 were determined as follows. The results are shown in Table 1. In addition, a wet bead mill SC50 (manufactured by Mitsui Mining Co., Ltd.) was used to mix 400 parts by mass of each inorganic powder with 600 parts by mass of ion-exchanged water, and the resulting slurry was dispersed at a rotation speed of 3,000 rpm for 10 minutes using 100 g of φ0.3 mm zirconia beads as a medium to prepare slurries (SA-1 to SA-7) in which inorganic powders made of silica-based inorganic compounds were dispersed.
The slurry in which inorganic powder FA-1 is dispersed is SA-1, the slurry in which inorganic powder FA-2 is dispersed is SA-2, the slurry in which inorganic powder FA-3 is dispersed is SA-3, the slurry in which inorganic powder FA-4 is dispersed is SA-4, the slurry in which inorganic powder FA-5 is dispersed is SA-5, the slurry in which inorganic powder FA-6 is dispersed is SA-6, and the slurry in which inorganic powder FA-7 is dispersed is SA-7.

<Method for measuring average primary particle size>
Photographs of the powder were taken at magnifications of 5,000 to 100,000 times using a scanning electron microscope ("XL-30S" manufactured by Philips), and the photographed images were processed using image analysis software ("IP-1000PC", product name; manufactured by Asahi Kasei Engineering Corporation). The average primary particle size was determined based on the measured value of the number of particles (100 or more) observed within a unit field of view of the photograph.

<Method for measuring the zeta potential of inorganic powders and granules>
The inorganic powder particles were suspended in ion-exchanged water of pH 7, and dispersed in water by irradiating ultrasonic waves for 30 minutes so that the concentration of the suspension water was 1.0 mass%. The zeta potential of this suspension water was measured using a zeta potential measuring device ("ELSZ-2000" manufactured by Otsuka Electronics Co., Ltd.). The same sample was measured three times, and the average was taken as the zeta potential.

(2) Inorganic powder (B) composed of crystalline rare earth metal fluoride By carrying out mechanochemical treatment on the inorganic powder (YbF ₃ -40, YbF ₃ -200 and YbF ₃ -300) composed of each of the crystalline rare earth metal fluorides, slurries (SB-1 to SB-5) in which the inorganic powder (B) was dispersed were obtained.
The mechanochemical treatment was carried out by using a wet bead mill SC50 (manufactured by Mitsui Mining Co., Ltd.) to disperse a slurry of 600 parts by mass of ion-exchanged water mixed with 400 parts by mass of inorganic powder particles of each crystalline rare earth fluoride, using 100 g of φ0.3 mm zirconia beads as a medium at a rotation speed of 3000 rpm for the treatment time shown in Table 2.
The obtained slurry was dried under reduced pressure using an evaporator to prepare inorganic powders (B); FB-1 to FB-5, with the material of the crystalline rare earth metal fluoride particles and the processing time of the dispersion treatment as shown in Table 2. The average primary particle size and zeta potential of the obtained inorganic powders were measured in the same manner as in (1) above, and the 2θ and full width at half maximum (°) of the peak of the crystal plane (1,1,1) in the X-ray diffraction pattern were measured as follows. The results are shown in Table 2.

<Method of measuring 2θ and full width at half maximum (°) of crystal plane (1,1,1)>
The powder was filled on a sample stage and measured with an X-ray diffractometer ("Smartlab" manufactured by Rigaku Corporation) to obtain an X-ray diffraction pattern (chart) with 2θ (°) on the horizontal axis and diffraction intensity on the vertical axis. CuKα rays were used as X-rays for the X-ray diffraction measurement.
When the material of the crystalline rare earth metal fluoride particles is _YbF3 , the peak with the greatest intensity is the peak due to the (1,1,1) plane (the peak observed around 2θ = 28°), so the full width at half maximum (°) of this peak was obtained.

(3) Preparation of inorganic powder (C) composed of agglomerated particles (FC-1 to FC-16)
100 g of the slurry SA-2 and 25 g of the slurry SB-2 were mixed to obtain a mixed slurry. Next, 1.6 g (0.006 mol) of γ-methacryloyloxypropyltrimethoxysilane and 20 g of water were added, and then acetic acid was added to adjust the pH to 4, and the mixture was stirred for 1 hour and 30 minutes to obtain a uniform solution. This solution and ion-exchanged water (50 g) for adjusting the concentration were added to the mixed slurry and mixed uniformly. Then, while lightly mixing the dispersion, the inorganic powder dried by the spray drying method was collected from the cyclone collection section and the collection section under the main body. The spray dryer used was a spray dryer (spray dryer "FOC-20", manufactured by Okawara Kakoki). The disk rotation speed was 26,000 rpm, and the temperature of the drying atmosphere air was 200 ° C. Then, the inorganic powder collected from the cyclone collection section was vacuum dried at 80 ° C. for 17 hours to obtain inorganic powder (C): FC-1. The inorganic powder recovered from the recovery section below the main body was similarly vacuum dried to obtain inorganic powder (C): FC-2.

Inorganic powders (C): FC-3 to FC-13 were prepared in the same manner as FC-1, except that the types and ratios of the slurry of silica-based inorganic compound and the slurry of crystalline rare earth metal fluoride used in the preparation of inorganic powders (C) and the amount of ion-exchanged water added for concentration adjustment were changed as shown in Table 3.
When a slurry (SA-6, SA-7) in which inorganic powder particles (FA-6, FA-7) composed of a silica-based composite oxide that does not satisfy the requirements of the present invention were dispersed was used, or when the amount of crystalline rare earth metal fluoride was small and the viscosity of the slurry was high, the slurry clogged the nozzle during spray drying, making it impossible to spray (FC-14 to FC-16).
The average agglomerated particle size (median size in volume-based particle size distribution) of the obtained inorganic powder or particle (C) was measured as follows.
The formation of aggregated particles in the inorganic powder (C) was confirmed by a scanning electron microscope.

(FC-17)
100 g of the slurry SA-2 and 100 g of the slurry SB-2 were mixed to obtain a mixed slurry. Next, 1.6 g (0.006 mol) of γ-methacryloyloxypropyltrimethoxysilane and 20 g of water were added, and then acetic acid was added to the mixture so that the pH was 4, and the mixture was stirred for 1 hour and 30 minutes to obtain a uniform solution. 100 g of the mixed slurry and ion-exchanged water for adjusting the concentration were added to this solution, and the mixture was mixed uniformly. Thereafter, while the dispersion was lightly mixed, the inorganic powder (C) dried by the spray drying method was collected from the cyclone collection section and the collection section under the main body.
The spray dryer used was a spray dryer (Spray Dryer "RL-8", manufactured by Okawara Kakoki). The spray pressure was 0.20 MPa, and the temperature of the drying atmosphere air was 200°C. Thereafter, the inorganic powder recovered from the cyclone recovery section was vacuum dried at 80°C for 17 hours to obtain 65 g of inorganic powder (C): FC-17 composed of agglomerated particles.
The average agglomerated particle size (median size in volume-based particle size distribution) of the obtained inorganic powder or particle (C) was measured as follows.
The formation of aggregated particles in the inorganic powder (C) was confirmed by a scanning electron microscope.

<Method for measuring average agglomerated particle size>
0.1 g of inorganic powder composed of aggregated particles was dispersed in 10 mL of ethanol and thoroughly shaken by hand. The median diameter of volume statistics was determined using a particle size distribution analyzer ("LS230", manufactured by Beckman Coulter) using a laser diffraction-scattering method and the optical model "Fraunhofer".

The average value of the total mass of the crystalline rare earth metal fluoride (inorganic particles (b)) relative to 100 parts by mass of the total mass of the silica-based inorganic compound (inorganic particles (a)) contained in each of the individual agglomerated particles constituting the obtained inorganic powder (FC-1) was 25 parts by mass, which corresponds to the value shown in Table 3. Similarly, the average value of the total mass of the crystalline rare earth metal fluoride (inorganic particles (b)) relative to 100 parts by mass of the total mass of the silica-based inorganic compound (inorganic particles (a)) for the other inorganic powders (FC-2 to FC17) corresponds to the value shown in Table 3.
The concentrations (% by mass) shown in Table 3 refer to the concentrations (% by mass) of the inorganic powder particles in the mixed slurry used in the spray drying.

(4) Regarding the organic-inorganic composite powder (D) composed of inorganic powder (A) composed of silica-based composite oxide and organic-inorganic composite particles composed of a composite material of resin, 100 g of the inorganic powder (FA-2) was added to 200 g of ion-exchanged water, and a water dispersion (dispersion of inorganic powder) was obtained using a circulation type grinder SC Mill (manufactured by Nippon Coke Engineering Co., Ltd.). Next, 4 g (0.016 mol) of γ-methacryloyloxypropyltrimethoxysilane and 0.003 g of acetic acid were added to 80 g of water and stirred for 1 hour and 30 minutes to obtain a uniform solution with a pH of 4. This solution was added to the dispersion of the inorganic powder and mixed until it was uniform. Thereafter, the dispersion was lightly mixed and supplied onto a disk rotating at high speed, and granulated by a spray drying method. The spray drying was performed using a spray dryer TSR-2W (manufactured by Sakamoto Giken Co., Ltd.) equipped with a rotating disk and atomized by centrifugal force. The rotation speed of the disk was 10,000 rpm, and the temperature of the drying atmosphere air was 200° C. Thereafter, the powder obtained by granulation by spray drying was vacuum dried at 60° C. for 18 hours, and 73 g of a powder granule (agglomerated powder granule) composed of approximately spherical aggregated particles was obtained.
Next, 30 g of the aggregated powder was immersed in a polymerizable monomer solution containing 7 g of UDMA as a polymerizable monomer, 0.015 g of azobisisobutyronitrile (AIBN) as a thermal polymerization initiator, and 12.4 g of ethanol as an organic solvent. After thorough stirring, the mixture was allowed to stand for 1 hour after confirming that it had become a slurry. The mixture was dried for 1 hour using a vacuum dryer under conditions of a reduced pressure of 10 hectopascals and a heating condition of 40°C to remove the organic solvent. When the organic solvent was removed, a powder with no aggregation and high fluidity was obtained.
The powder was heated for 20 minutes under conditions of a reduced pressure of 10 hectopascals and 140° C. to polymerize and harden the polymerizable monomer in the powder. Then, the mixture was sieved through a 100 μm mesh to obtain 26 g of organic-inorganic composite powder (D): FD-1, which was composed of approximately spherical organic-inorganic composite particles in which the surfaces of the obtained spherical aggregates were coated with an organic polymer.

An organic-inorganic composite powder/particle: FD-2 was obtained in the same manner as in FD-1, except that the amount of the polymerizable monomer UDMA used was changed to 4.1 g.
An organic-inorganic composite powder/particle: FD-3 was obtained in the same manner as in FD-1, except that the amount of the polymerizable monomer UDMA used was changed to 16 g.
An organic-inorganic composite powder/particle: FD-4 was obtained in the same manner as in the preparation of FD-1, except that the amount of the polymerizable monomer UDMA used was changed to 1.6 g.
An organic-inorganic composite powder/particle: FD-5 was obtained in the same manner as in the preparation of FD-1, except that the amount of the polymerizable monomer UDMA used was changed to 22.6 g.
When sieving was performed in the production of FD-1, the powder recovered from the sieve was designated as organic-inorganic composite powder/grain: FD-6.
FD-6 was pulverized using a vibration ball mill to obtain organic-inorganic composite powder particles: FD-7 to FD-9 having different average particle sizes.
The average particle size (median size in the volume-based particle size distribution) of the obtained organic-inorganic composite powder (D) was determined as follows. The results are shown in Table 4.

<Evaluation of the average particle size of organic-inorganic composite powder>
0.1 g of the organic-inorganic composite powder (D) was dispersed in 10 mL of ethanol and irradiated with ultrasonic waves for 20 minutes. Using a particle size distribution analyzer "LS230" (manufactured by Beckman Coulter, Inc.) using a laser diffraction-scattering method, the average particle size was calculated from the median diameter of volume statistics using the optical model "Fraunhofer."

3. Examples and Comparative Examples <Example 1>
A polymerizable monomer solution was prepared by completely dissolving 0.20 parts by mass of CQ and 0.5 parts by mass of DMBE as a polymerization initiator in a polymerizable monomer consisting of 60 parts by mass of UDMA and 40 parts by mass of 3G. Then, 140 parts by mass of inorganic powder (A) FA-2, 93 parts by mass of inorganic powder (C) FC-4, and the polymerizable monomer solution were kneaded in a mortar until uniform and made into a paste, and then degassed to prepare a paste-like dental hardenable composition. The prepared paste-like dental hardenable composition was filled into a cylindrical syringe, and a plunger for pushing out the contents of the syringe and a cap were attached. Then, one of the syringes filled with the prepared dental hardenable composition was stored in an incubator at 50 ° C. for one week.
The obtained dental curable compositions were evaluated for flowability in a paste state, consistency, dispersibility of the crystalline rare earth metal fluoride in the curable composition, contrast ratio, bending strength, and discharge feeling by the methods described below.
The flowability was evaluated for the dental curable composition immediately after preparation and for the dental curable composition stored at 50° C. for one week, with the evaluation result immediately after preparation being taken as the “initial” value (initial value) and the evaluation result after one week of storage at 50° C. being taken as the “after storage” value (after storage value). The results are shown in Table 5.

<Method of measuring flowability>
A 20G needle tip was attached to the tip of the syringe filled with the prepared dental hardenable composition in paste form. Then, after leaving it for 30 minutes in a thermostatic chamber at 25°C, a circle with a diameter of 5 mm was drawn on a glass plate in advance, 0.1 g of the dental hardenable composition was discharged into the circle, and the plate was left in a horizontal state for 2 minutes in an incubator at 37°C. The vertical and horizontal diameters of the paste were measured for spread at that time, and the average of both values was calculated. The evaluation was performed twice, and the average value was taken as the flowability of the paste. In addition, the degree of change due to storage was evaluated for fluidity by taking {(value after storage-initial value)/initial value}×100 as the rate of change (%).

<Method of measuring consistency>
The prepared dental hardenable composition in paste form was left in an incubator at 45°C for 1 day, and then left at 25°C for 30 minutes to measure the consistency of the paste by the following method. 0.2 g of paste was weighed out onto a polypropylene film, with the center raised. A polypropylene film, a glass plate, and a weight (50 g in total) were placed on top of the paste in this order, and after 10 seconds, the glass plate and weight were removed. The vertical and horizontal diameters of the paste at this time were measured through the polypropylene film, and the average of both was calculated. The above evaluation was performed twice, and the average value was taken as the consistency of the paste.

<Method for Evaluating Dispersibility of Crystalline Rare Earth Metal Fluoride Particles in Dental Hardenable Composition>
The dental curable composition thus prepared was placed in a mold having a through hole of 7 mmφ×1 mm, and a polyester film was pressed onto both sides, after which the polyester film was peeled off from only one side, and the peeled side was irradiated with light from a dental light irradiator (Eliper Deep Cure, manufactured by 3M) at a distance of 3 mm for 20 seconds. After the dental curable composition was cured, it was removed from the mold, placed in 10 mL of ethanol, and treated with ultrasonic waves for 20 minutes. The obtained cured product was fixed with carbon tape on a sample stage with the light irradiated surface facing up, and a measurement sample was prepared by subjecting the sample to conductive treatment (platinum vapor deposition). The backscattered electron image of this measurement sample was observed at a magnification of 1,000 times using a scanning electron microscope (manufactured by JEOL Ltd., "JSM-7800F PRIME"), and the number of bright particles of 3 μm or more observed within the unit field of view of the photograph was counted.
A: No bright particles of 3 μm or more are observed within the unit visual field of a scanning electron microscope. B: Bright particles of 3 μm or more are observed within the unit visual field of a scanning electron microscope.

<Method for evaluating contrast ratio (Yb/Yw) of dental curable composition cured product>
The dental curable composition thus prepared was placed in a mold having a through hole of 7 mmφ×1 mm, and polyester films were pressed onto both sides. Next, the distance was adjusted so that the irradiation intensity on the surface of the polyester film was 1000 mW/ ^cm2 , and both sides were irradiated with light for 20 seconds each using a dental light irradiator (Eliper Deep Cure, manufactured by 3M). After the dental curable composition was cured, it was removed from the mold, and the tristimulus value Y value (background color black and white) of the cured product was measured using a color difference meter (Tokyo Denshoku "TC-1800MKII"). The following formula,
Contrast ratio (Yb/Yw)=Y value when background color is black/Y value when background color is white. The contrast ratio (Yb/Yw) was calculated based on this.

<Method of measuring "flexural strength">
The dental curable composition paste was filled into a stainless steel mold and pressed against a polypropylene film, and then irradiated with light from one side for 30 seconds x 3 times using a visible light irradiator (Eliper Deep Cure, manufactured by 3M Co.) by moving the location so that the entire surface was exposed to light and adhering to the polypropylene film. Then, the opposite side was also irradiated with light for 30 seconds x 3 times to obtain a cured product. The cured product was trimmed into a 2 x 2 x 25 mm square column shape using #1500 waterproof abrasive paper, and this sample piece was mounted on a tester (Shimadzu Corporation "Autograph AG5000D") to measure the three-point bending fracture strength at a support distance of 20 mm and a crosshead speed of 1 mm/min, and a load-deflection curve was obtained, and the bending strength was calculated from the following formula. Five test pieces were evaluated, and the average value was taken as the bending strength.
Formula: σB=(3PS)/(2WB ² )
The symbols in the above represent, respectively, σB: bending strength (Pa), P: load at the time of fracture of the test piece (N), S: distance between supports (m), W: width of the test piece (m), and B: thickness of the test piece (m).

<Evaluation of the feeling of ejection>
A 20G needle tip was attached to the tip of the syringe container, and 0.2 g of paste was discharged from the tip of the needle tip onto a glass plate (5 cm x 10 cm) by pressing the plunger. The ease of pressing the plunger at this time was confirmed, and the discharge feeling of the paste was evaluated according to the following evaluation criteria. Note that a discharge feeling of 1 to 3 was considered to be an acceptable product.
1: Paste can be ejected even when pressed lightly, and ejection properties are very good. 2: Paste can be ejected without difficulty, and ejection properties are good. 3: Paste can be ejected by pressing a little harder, and ejection properties are acceptable. 4: Paste can be ejected by pressing hard, but ejection properties are poor. 5: Paste cannot be ejected at all.

<Examples 2 to 28 and Comparative Examples 1 to 8>
Paste-like dental curable compositions were prepared in the same manner as in Example 1, except that the polymerization monomer (M), inorganic powder particles (A), inorganic powder particles (B), inorganic powder particles (C), and organic-inorganic composite powder particles (D) used were changed as shown in Tables 5 to 8, and the obtained compositions were evaluated in the same manner as in Example 1. The results are shown in Tables 5, 6, 7, and 8.

As can be seen from the results of Examples 1 to 28, when inorganic powders and organic-inorganic composite powders satisfying the requirements of the present invention are used, the crystalline rare earth metal fluoride is sufficiently dispersed in the hardenable composition, and the change in fluidity over time is small. Figure 2 shows a photograph of the hardened product of the dental hardenable composition of Example 1 observed with a scanning electron microscope, and no bright particles of 3 μm or more were confirmed, indicating that the dispersibility of the crystalline rare earth metal fluoride is good.
As can be seen from the results of Comparative Examples 1 and 2, when the amount of inorganic powder (B), regardless of the content form, does not satisfy the requirements of the present invention, a decrease in strength and a deterioration in the feeling of ejection, or a large change in fluidity over time due to storage, is observed.
As can be seen from the results of Comparative Example 3, when the inorganic powder (C) does not satisfy the requirements of the present invention, the crystalline rare earth fluoride particles are not sufficiently dispersed in the hardenable composition, and a large change in fluidity over time is observed during storage.
As can be seen from the results of Comparative Examples 4 to 7, when the organic-inorganic composite powder (D) does not satisfy the requirements of the present invention, the strength of the hardened body of the dental hardenable composition decreases or the feeling of discharging becomes poor.
3 shows a photograph of the hardened product of the dental hardenable composition of Comparative Example 8 taken with a scanning electron microscope, in which bright particles of 3 μm or more were observed, indicating that the dispersibility of the crystalline rare earth metal fluoride was poor. As can be seen from this result, when the inorganic powder (B) was directly added, aggregated particles remained in the hardenable composition and were not sufficiently dispersed, resulting in a large change in fluidity over time.

Claims (12)

a polymerizable monomer (M): 100 parts by mass; and an inorganic powder/granule (C) comprising agglomerated particles (c) including a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential when measured in water, and an average primary particle diameter of 50 nm to 1 μm when measured by an electron microscope, and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, and an inorganic powder/granule (B) comprising agglomerated particles (c) including the inorganic particles (a) and an inorganic powder/granule (B) having an average primary particle diameter of 1 to 300 nm when measured by an electron microscope,
the average value of the total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) contained in each of the aggregate particles (c) constituting the inorganic powder or granule (C) is within a range of 20 to 300 parts by mass;
Inorganic powder or grain (C): 10 to 100 parts by mass, having an average agglomerated particle size of 1 to 50 μm, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method;
A composition comprising:
The composition further comprises at least one of the inorganic powder (A) and the organic-inorganic composite powder (D),
the organic-inorganic composite powder (D) is constituted by organic-inorganic composite particles (d) made of a composite material of the inorganic powder (A) and a resin, the content of the inorganic powder (A) in the composite material being 60 to 90 mass %, and the organic-inorganic composite powder (D) has an average particle size of 1 to 100 μm, which is defined as the median size in a volume-based particle size distribution measured by a laser diffraction-scattering method;
A dental curable composition, characterized in that a total content of the inorganic powder and granules (A) in the composition, regardless of the form of inclusion, is 170 to 270 parts by mass, and a total content of the inorganic powder and granules (B), regardless of the form of inclusion, is 5 to 50 parts by mass. The dental curable composition according to claim 1, wherein the inorganic particles (b) are uniformly dispersed in the inorganic particles (a) in each aggregate particle (c) constituting the inorganic powder (C). The dental hardenable composition according to claim 1, wherein the inorganic particles (a) are made of a silica-based inorganic compound, and the inorganic particles (b) are made of a crystalline rare earth metal fluoride. The dental hardenable composition according to claim 3, wherein the full width at half maximum of the maximum intensity peak derived from the crystalline rare earth metal fluoride in the X-ray diffraction pattern obtained when X-ray diffraction measurement is performed on the inorganic powder (B) is 0.3° or more. The dental curable composition according to claim 1, wherein the inorganic powder (C) is obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium, and spray-drying the resulting homogeneous mixed slurry. The polymerizable monomer (M),
The inorganic powder (C),
The method for producing a dental hardenable composition according to claim 1 , comprising mixing at least one of the inorganic powder and particles (A) and the organic-inorganic composite powder and particles (D). The method for producing a dental curable composition according to claim 6, wherein the inorganic powder (C) is produced by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder (A) is dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder (B) is dispersed in a dispersion medium, and spray-drying the resulting homogeneous mixed slurry. The method for producing a dental hardenable composition according to claim 7, wherein the mixed slurry does not contain an ionic surfactant. The method for producing a dental hardenable composition according to claim 7, wherein the concentration of the mixed slurry is less than 40% by mass. an inorganic powder/granule (C) comprising agglomerated particles (c) each including a plurality of inorganic particles (a) made of the same material and exhibiting a negative zeta potential when measured in water, and an average primary particle diameter measured by an electron microscope of 50 nm to 1 μm; and a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, and an inorganic powder/granule (B) comprising agglomerated particles (c) each including a plurality of inorganic particles (b) made of the same material and exhibiting a positive zeta potential when measured in water, and an average primary particle diameter measured by an electron microscope of 1 to 300 nm;
the average value of the total mass of the inorganic particles (b) per 100 parts by mass of the inorganic particles (a) contained in each of the aggregate particles (c) constituting the inorganic powder or granule (C) is within a range of 20 to 300 parts by mass;
An inorganic powder or granule having an average agglomerated particle size, defined as the median diameter in a volume-based particle size distribution measured by a laser diffraction-scattering method, of 1 to 50 μm, and containing no ionic surfactant. The method for producing inorganic powder particles according to claim 10, comprising a step of spray-drying a uniform mixed slurry obtained by mixing a slurry (Sa) in which 100 parts by mass of the inorganic powder particles (A) are dispersed in a dispersion medium with a slurry (Sb) in which 20 to 300 parts by mass of the inorganic powder particles (B) are dispersed in a dispersion medium, the mixed slurry not containing an ionic surfactant. The method for producing inorganic powders and granules according to claim 11, wherein the concentration of the mixed slurry is less than 40% by mass.

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